Hydrology and the Water Cycle

Hydrology is the scientific study of water on Earth, including its distribution, movement, and physical and chemical properties. It examines how water travels through the atmosphere, across the land surface, and underground, and how it interacts with soil, rock, and living things. As a discipline it underpins the management of water resources, flood prediction, and the understanding of climate and ecosystems.

Water has several unusual physical properties that shape its behaviour in nature. It is densest a few degrees above its freezing point, so ice floats and lakes freeze from the top down. It has a high capacity to absorb and release heat, which moderates climate, and a high surface tension that influences how it moves through soil and plants. Water is also an excellent solvent, carrying dissolved minerals and nutrients through the environment.

The hydrologic cycle describes the continuous circulation of water between the oceans, atmosphere, and land. Solar energy evaporates water from oceans, lakes, and soil, and transpiration releases water vapour from plants. This vapour rises, cools, and condenses into clouds, eventually falling back to the surface as precipitation such as rain or snow. Some of this water runs off into rivers and returns to the sea, while some soaks into the ground to recharge groundwater. The cycle has no beginning or end, and it links closely to weather, climate, and the broader study of the atmosphere.

Frequently asked questions

What does hydrology study?

It studies the occurrence, movement, distribution and properties of water on and below the Earth’s surface and in the atmosphere.

What are the main stages of the water cycle?

Evaporation and transpiration, condensation into clouds, precipitation, and the runoff and infiltration that return water to oceans and groundwater.

Why does ice float on water?

Water is densest just above freezing, so ice is less dense than liquid water and floats, allowing lakes to freeze from the surface down.